Prevention and removal of slime formations



Patented" den. 29, 1935 STAT Ksabella a. mans, recreate, N. it.

No Drawing. Application June 15, 1934,

5 Serial No. 730,756

a (cl. arc-2s) This invention provides a new and improved method for theprevention and removal of slime formationson the cooling surfaces ofcondensers such as are used commonly in public utility generatingstations. Thisslime or scum forms on the inner surface of the condensertubes and acts as an insulator, thus reducing the heat transfer andseriously affecting the vacua obtainable inthe condenser.

The methods in use at the present time are: (i) To shut down the entireunit and remove. the slime mechanically by pushing rubber plugs throughthe tubes or by various methods of brushing and boiling the tubes. ingthe condenser out of service periodically and increases the cost oflabor materially. (2) To treat the water with chlorine intermittently,under encapsulated bacteria.

mechanical control. This latter methodawill be discussed below ingreater detail.

Although this invention is described for use in condensers, it isobvious that the principles may be employed whenever the prevention andremoval of slime formations on surfaces in contact with water areindicated.

It is generally accepted that the causes for these slime formationsoriginate in the water which is circulated through the condenser. Theseformations are composed usually of encapsulated bacteria, iron bacteria,algaeand much mineral matv ter which has become entangled in thefilaments of the iron bacteria and the zooglea iormed by the Idiscovered that there exists a sequential symbiosis of the encapsulatedbacteria and the iron bacteria. I also discovered U that the acidproduction oi the former made poswaters which have a high organiccontent and therefore exhibit a high chlorine demand, meaning the amountnecessary to satisfy the capacity of the water to neutralize thechlorine. The amount to do this and leave a slight excess or residual isso great that it makes the cost of operation prohibitive. Unless largequantities of chicrine are used there is the danger that if the bacteriaare not completely killed the stronger ones will be revived when the rawwater is circulated This necessitates tal;-'

again and the residual chlorine is washed away.

Each time this is done the bacteria develop an increased tolerance forchlorine and soon are not affected by even higher concentrations.

I propose the use of chloramines instead of chlorine for the treatmentof the circulating water. Chloramines act germicidally more slowly thanchlorine and are, therefore, less rapid in early efiects, when used inequal concentration tochlorine. I have discovered, however, that evenwith a slight lag in the rate of onset of the destructive efiect of thechloramineson the film of bacteria their destructive effects onceinitiated are more vigorous and the final effects more nearly a totalityof destruction than has been obtained with the use of chlorine.

Waters of high organic content do not exhibit as high a demandiorchloramine as they do for chlorine, thus leaving the chloramine freer toact as a sterilizing agent and permitting lower doses to maintainresiduals longer. This in creases the efiectiveness of the disinfectantand reduces the amount necessary for sterilization.

After a film of slime has been removed by my treatment, it is desirableto subject the water to the treatment periodically, so that theformation. of new film is effectively prevented.

The treatment comprises the periodic intro= duction oi-chloramines(monochloramine NHaCldichloramine NHClz, and/or trichloramine N011) tothe Water at a point before it enters the condenser tubes. The amount ofchloramines and frequency of treatment are determined by the quality ofthe water, length of treatment, temperature, velocity and other variablefactors. As a rule it is sumcient to maintain a residual chloramine offrom 0.1 lie-1.0 parts per million in the eifiuent. The concentration ofchloramine and the length and ireoguency of the treatment are alsodetermined by the extent of contamination in the condenser and theresistance of the slime forming organisms in the water.

In carrying out this prpcess the chloraes may be formed of theconstituent gases in an aqueous medium and thenintroduced to the water,or they may be formed by injecting am- The ratio of ammonia to chlorineis dependent on the quality of the water, temperature, velocity andother variable factors but chloramines are usually formed when the ratiois 1:2 to 1:4 respectively. Chloramines are most eillcient in waterwhere the hydrogen ion concentration is between pH 6.0 and pH 8.0 butshow some activity on both the acid and alkaline sides of this range. g

I claim:

1. The method of preventing the deposit and growth of'slime-formingorganisms on the surfaces of condensers and heat exchange apparatus, incontact with flowing water or removing deposits already formed on suchsurfaces, which consists in adding chloramines to such flowing waterbefore it reaches such surfaces, the quantity of chloramines perunit ofwater immediately prior to contact thereof with such surfaces being suchthat the water after leaving such surfaces contains at least a smallquantity of residual chloramines, whereby said water is employed as adiluent for the chloramines and as a carrier for bringing saidchloramines into contact with said organisms.

2. The method of preventing the deposit and growth of slime-formingorganisms on the surconsists in adding chloramines to such flowing waterbefore it reaches such surfaces, the quantity of chloramines per unit ofwater immediately prior to contact thereof with such surfaces being suchthat the water after leaving such surfaces contains at least a smallquantity of residual chloramines, whereby said water is employed as adiluent for the chloramines and as a carrier for bringing saidchloramines into contact with said organisms, continuing this treatmentfor a period of time depending upon the resistance of theorganisms to bedestroyed and then interrupting the treatment until a new deposit oforganisms in deleterious quantity has been formed.

3. The method of preventing the deposit and growth of slime formingorganisms on surfaces in contact with flowing water or removing depositsalready formed on such surfaces, which consists in providing chloraminesin such water, the quantity of chloramines per unit of water immediatelyprior to its contact with such surfaces being such that the water afterleaving such surfaces contains residual chloramines, the quantity ofsuch residual chloramines being from approximately one-tenth part toapproximately ten parts of chloramines per million of'water.

ISABELLA B. ROMANS.

